Atlas triggers overview in MongoDB - Step-by-Step Execution

Concept Flow - Atlas triggers overview

Trigger Event Occurs

↓

Atlas Trigger Listens

↓

Evaluate Trigger Condition

↓

Run Trigger Function

↓

Perform Actions (DB ops, HTTP calls, etc)

↓

End

Atlas triggers listen for database or scheduled events, check conditions, and run functions to perform actions automatically.

Execution Sample

MongoDB

exports = function(changeEvent) {
  const doc = changeEvent.fullDocument;
  if (doc.status === 'active') {
    console.log('Active document:', doc);
  }
};

This trigger function runs when a document changes and logs it if its status is 'active'.

Execution Table

Step	Trigger Event	Condition Checked	Condition Result	Action Taken	Output
1	Document Inserted	doc.status === 'active'	True	Log document	Active document: { ... }
2	Document Updated	doc.status === 'active'	False	No action	No output
3	Document Updated	doc.status === 'active'	True	Log document	Active document: { ... }
4	Scheduled Trigger Fires	No condition	N/A	Run scheduled function	Performed scheduled task
5	No Event	N/A	N/A	No action	No output

💡 Execution stops when no trigger event occurs or condition is false.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
changeEvent.fullDocument.status	undefined	active	inactive	active	N/A	N/A
conditionResult	undefined	true	false	true	N/A	N/A
action	none	log	none	log	scheduled task	none

Key Moments - 2 Insights

Why does the trigger not run any action when the condition is false?

Because the trigger function checks the condition (doc.status === 'active') and only runs the action if true, as shown in execution_table rows 2 and 5.

What happens when a scheduled trigger fires without a condition?

The trigger runs its function automatically without checking conditions, performing scheduled tasks as in execution_table row 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the action taken at step 2?

A No action

B Run scheduled function

C Log document

D Insert document

💡 Hint

Check the 'Action Taken' column for step 2 in the execution_table.

At which step does the trigger run a scheduled function?

A Step 3

B Step 4

C Step 1

D Step 5

💡 Hint

Look for 'Scheduled Trigger Fires' in the 'Trigger Event' column.

If the document status is 'inactive', what will the trigger do?

A Log the document

B Run scheduled function

C Do nothing

D Insert a new document

💡 Hint

Refer to variable_tracker for 'changeEvent.fullDocument.status' and execution_table rows where condition is false.

Concept Snapshot

Atlas triggers listen for database or scheduled events.
They check conditions on event data.
If conditions are true, they run functions.
Functions can perform DB operations, HTTP calls, or logs.
Scheduled triggers run functions on a timer without conditions.
Triggers automate responses to data changes or schedules.

Full Transcript

Atlas triggers in MongoDB Atlas automatically respond to database events or scheduled times. When an event like a document insert or update happens, the trigger listens and checks a condition, such as if a document's status is 'active'. If the condition is true, the trigger runs a function that can log information, update data, or call external services. Scheduled triggers run functions at set times without conditions. This automation helps keep your database reactive and integrated with other systems without manual intervention.